Manufacturing technique of powder metallurgy

ABSTRACT

The manufacturing technique for powder metallurgy of the invention includes the steps of: mixing ceramic powder with binders, fillings or lubricants for casting a body; forming a microwave-absorbent body using molding, extrusion, forging, injection or doctor blade; placing the body into a microwave oven for heating and debinding; placing the half-finished product after debinding in a sintering oven for sintering the debinded half-finished product; and finally obtaining a finished product after sintering and temperature lowering.

BACKGROUND OF THE INVENTION

[0001] (a) Field of the Invention

[0002] The invention relates to a manufacturing technique of powdermetallurgy, and more particularly, to a manufacturing technique ofpowder metallurgy for accelerating the production procedure, andreducing equipment and resource cost thereof, as well as being capableof quickly drying and removing binders, fillings or lubricants in orderto suit ceramic material fabrications.

[0003] (b) Description of the Prior Art

[0004] In common manufacturing processes of powder metallurgy, in orderto facilitate ceramic powder to form a green body more easily,macromolecules are frequently added as a forming additive. Such type offorming additives includes binders, surfactants, fillings or lubricants.The forming additives are mixed with macromolecules for casting bodiesthat may be formed by such as molding, forging, extrusion, injectionmolding or doctor blade methods. Then the green bodies are placed intofurnaces for debinding as the next step.

[0005] Injection molding from ceramic powder possess properties ofgeneral plastic injections, and are materials that can be used with highefficiency. When injection moldings from ceramic powder are adopted forproducts having complicated shapes in mass production, the products haverelatively better microstructures because sizes thereof are evenlycontracted. Therefore, the injection molding products approach near netshapes or net shapes, and do not require a great amount of subsequentprocessing, and thus significantly saving production cost thereof byreducing the processing expenses. However, the binder used come as highas 30 vol%, and defects incurred are prone to arise during removingmacromolecules in the debinding process; to be more precise, thedebinding process stands as a rather major manufacturing process.

[0006] In the present invention, issues like green body forming,sintering, materials of powder, or ingredients of additives shall not bediscussed. Instead, the invention is targeted at providing anothermethod for the debinding step in the manufacturing process.

[0007] As described above, common debinding processes currently usedinclude solvent debinding and thermal debinding, wherein:

[0008] 1. Solvent debinding is implemented by the steps of dipping abody into a solvent, and extracting dissolvable binders, fillings,surfactants or lubricants from the body. However, such means of solventdebinding brings about environmental and recycling issues and thusfurther increases the processing expense thereof.

[0009] 2. Thermal debinding is implemented by the steps of placing abody into a furnace, and eliminating any binders using a hightemperature to remove binders, fillings, surfactants, lubricants ormacromolecules in sequence. This method may be used to remove bindersdirectly or after solvent debinding with only human-friendly gasesproduced that give no environmental, recycling or human-hazardous issuesas the solvent debinding, and is therefore the most extensively applieddebinding process. Nevertheless, it is necessary to pre-heat thefurnaces to a temperature required for thermal debinding, meaning thatthe time and energy of pre-heating and the energy consumed duringmaintaining the heat sum up to considerable amounts of money, and thusresulting in an efficiency problem often abstained by the manufacturingprocess. Also, defects are prone to occur during the time-consumingthermal debinding process, and hence reforms with respect to the aboveshortcomings can yet be advanced.

[0010] Furthermore, the modern times is an environmental-friendly era,especially regarding to uses and recycling of resources. It shall betaken into consideration that chemical solvent, which isnon-eco-friendly and is limited to a certain number of times to be used,is adopted for solvent debinding; and furnaces employed for thermaldebinding are quite energy consuming. Therefore, it is a vital task ashow to provide a manufacturing technique for debinding capable ofrapidly accomplishing the debinding process and reducing resourcewastage, as well as being environmental-friendly.

[0011] With respect of the aforesaid shortcomings, domestic andinternational patent publications or related information are taken intoreference. Referring to Patent Publication No. 333482, “ManufacturingProcess for Carbon Chromium/Aluminum Oxide Ceramic Devices HavingComplicated Shapes Using Injection Molding Technique”, it is observedthat several defects are derived from the debinding process thereof:

[0012] 1. The furnaces are troublesome and time-consuming in raising andlowering the temperatures thereof. The production cost can be reducedand the manufacturing efficiency can be elevated if the time of heatingfrom room temperature to a temperature required for debinding andlowering temperature after debinding completed can be shortened.

[0013] 2. Energy cannot be concentrated entirely on the body. Duringheating of a common furnace, a major part of the energy is absorbedthrough the furnace body and dissipated into the atmosphere, and thusleaving as little as 30 percent of the original energy for debinding thebody. It is indeed uneconomical to waste such great amounts of energyfor merely achieving the purpose of debinding.

[0014] 3. Common furnaces take up large spaces for that they are massivein volume and heavy in weight, and difficulties may arise for movingsuch furnaces, thus lacking mobility.

[0015] 4. Furnaces have high equipment cost. Expense burdens andmaintenance fees thereof may be worsened by problems and shortening oflifespan of heating bodies and heat-resistant materials caused by anycontamination of binder decompositions in the furnaces.

[0016] 5. Chemical solvents are limited to certain expiration periods.In solvent debinding, chemical extraction properties of chemicalsolvents are inevitably lowered after using for a period of time or whenincreasing the number of bodies. Besides, expired chemical solvents maybecome another environmental dilemma.

[0017] In addition, referring to Patent Publication No. 167524disclosing a method for thermal processing unstable ceramics usingmicrowave, wherein microwave technique is applied during the sinteringprocess of ceramics. In the prior invention, a microwave sensor isformed from an appropriate powder bed that is characterized regarding toheating, protection, deoxidization and thermal conductance as required.However, the characteristics are provided for the requirements of the“sintering” process of ceramics; that is, this prior invention confersnothing upon the “debinding” process of ceramic bodies before thesintering process. Therefore, the shortcomings of the aforesaiddebinding means (solvent debinding and thermal debinding) are notresolved by the Patent Publication No. 167524.

[0018] Conclusive from the above, as described by shortcomings andissues of the conventional debinding means, the handling of the solventused are troublesome, uneconomical and non-eco-friendly, and furnacesadopted for thermal debinding are time-consuming for heating andtemperature lowering. Therefore, it is a vital task of the invention ashow to provide a manufacturing technique for powder metallurgy capableof overcoming the prior disadvantages such as having high production andequipment cost, lack of mobility and being unable to concentrate energy.

SUMMARY OF THE INVENTION

[0019] The primary object of the invention is to provide manufacturingtechnique capable of accelerating production procedure, reducingproduction cost, and rapidly drying and removing binders, fillings orlubricants. The technique is suitable for debinding of cast bodies afterpowder materials are mixed with binders, fillings or lubricants, and isable to avoid energy waste in heating and temperature lowering as wellas keeping away from being bulky in size.

[0020] Another object of the invention is to provide manufacturingequipment and method for elevating manufacturing efficiency byshortening the time of heating and temperature lowering.

[0021] Another object of the invention is to provide manufacturingequipment and method with energy concentration for saving energy.

[0022] The other object of the invention is to provide manufacturingequipment and method with low equipment cost and mobility for reducingproduction cost and facilitating the moving thereof.

[0023] To better understand the manufacturing process and functions ofthe present invention, descriptions shall be given with the accompanyingdrawings below.

BRIEF DESCRIPTION OF THE DRAWINGS

[0024]FIG. 1 shows a schematic drawing illustrating the manufacturingprocess according to the invention.

[0025]FIG. 2 shows a comparison diagram illustrating the time requiredfor heating to sintering temperatures of the invention and a prior art.

[0026]FIG. 3 shows a comparison table illustrating the compressiveresistance of relative densities after sintering by the presentinvention and a prior art.

[0027]FIG. 4 shows manufacturing flow diagrams for comparing timerequired for debinding in the present invention and a prior art.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0028] Referring to FIG. 1, the manufacturing method implementing themanufacturing technique for powder metallurgy according to the inventioncomprises the steps of:

[0029] a. forming a body 1; the body 1 is formed by mixing ceramicpowder with binders, fillings or lubricants, and then by performing castmethods such as molding, extrusion, injection or scraping;

[0030] b. heating and debinding; the body 1 is embedded into a nonmicrowave-absorbent medium 2 placed in a crucible 3 so as to promotecapillarity thereof using the medium 2, and is then placed into amicrowave oven 4 for heating and debinding according to time andtemperature required for heating and debinding;

[0031] c. sintering; a half-finished product 4 is put in a sinteringoven 6 for sintering the degreased, half-finished product 4;

[0032] d. finishing product; temperature is lowered according to generalprocedures, and a finished product 7 is obtained from the originallyhalf-finished product 5 placed in the sintering oven 6.

[0033] According to the invention, the technique provided lies mainly inthe heating and debinding stage, and the characteristics thereof are:

[0034] before entering the debinding process, the microwave-absorbentbody 1 is placed in the microwave oven 4 and debinded by using adjustedmicrowave frequency required, and direct observations through a windowmay be carried out during the debinding process; in addition, thedegreased half-finished product 5 using microwave or a degreased bodyobtained by other methods is directly heated to the sinteringtemperature using microwave, and is then placed into the sintering oven6 after having reached the sintering temperature or sintered directly bymicrowave, and thus saving time and resources for gradual heating;referring to FIGS. 2 showing a comparison diagram illustrating the timerequired for heating to sintering temperatures of the invention and aprior art, and FIG. 3, tests at sintering temperatures 1400°0 C. and145020 C. are performed for a duration of two hours, and when comparingthe relative densities of the present invention to the prior art, it isclearly observed that the product from the invention has excellentsintering densities; also, referring to FIG. 4 showing time differencesfor debinding in the manufacturing process, the time for debindingaccording to the invention is merely half of that of the prior art, andthus effectively reducing the production time thereof.

[0035] It is perceived from the above that, the appeal according to theinvention is aimed at heating by microwave for accomplishing thedebinding process. The technique provided by the invention is capable ofovercoming disadvantages existing in the prior art: 1. inconvenientheating and temperature lowering of furnaces, and lengthened productiontime; 2. distracted heating energy, and uneconomical; 3. furnaces bulkyin size with poor mobility; 4. inefficiency and environmental issues ofchemical solvent. According to the invention, the method and equipmentprovided are able to accelerate production process, reduce productioncost, rapidly remove binders, fillings or lubricants, as well as beingenvironmental friendly for that the medium can be used for absorbingmicrowave for a multiple of times. Therefore, the invention is totallysuitable for debinding process of cast bodies from mixing ceramic powderwith binders, fillings or lubricants.

[0036] In addition, the microwave-absorbent cast bodies mentioned above,the ceramic powder contained therein may be carbon, carbide, nitride,titanate, oxide, sulfide or a compound: wherein the carbide may be SiC,TiC or WC; the nitride may be TiN, AIN or Si₃N₄; the titanate may bebarium titanate, calcium titanate, strontium titanate or lead titanate;the oxide may be NiO, CoO, CaMnO₃, LaMnO₃, SnO₂, TiO₂, MgWO₄, MgO, NiO,SrTiO₃ or SrZrO₃; the sulfide may be FeS or MnS; the compound may beFe₂O₃—MeO, wherein the Fe₂O₃ may be mixed with NiO, CoO, MoO, MgO, ZnO,CuO, Li₂O, CaO, FeO, B₂O, PbO, SrO, La₂O₃, Cr₂O₃, SnO₂ or WO₃, and NiO,CoO, MoO, MgO, ZnO, CuO, Li₂O, CaO, FeO, B₂O, PbO, SrO, La₂O₃, Cr₂O₃,SnO₂ or WO₃ may be used independently or mixed with others; in addition,the aforesaid nitride may be added with compounds such as Li₂O, La₂O₃,CaO, SrO, TiO₂, Sb₂O₅, Ta₂O₅ or Cr₂O₃.

[0037] It is of course to be understood that the embodiment describedherein is merely illustrative of the principles of the invention andthat a wide variety of modifications thereto may be effected by personsskilled in the art without departing from the spirit and scope of theinvention as set forth in the following claims.

What is claimed is:
 1. A manufacturing technique for powder metallurgycomprising the steps of: mixing ceramic powder with binders, fillings orlubricants for casting a body; forming a microwave-absorbent body usingmolding, extrusion, forging, injection or doctor blade; placing the bodyinto a microwave oven for heating and debinding; placing thehalf-finished product after debinding in a sintering oven for sinteringthe debinded half-finished product; obtaining a finished product aftersintering and temperature lowering; and the characteristics thereof are:before the body enters the debinding process, the body is placed in amicrowave-absorbent medium, and the body along with the medium areplaced in the microwave and debinded with adjusted temperature and timerequired.
 2. The manufacturing technique for powder metallurgy inaccordance with claim 1, wherein the half-finished body after debindingor a debinded body acquired from other methods is directly placed in themicrowave oven for heating to the sintering temperature, and is put in asintering oven having reached the sintering temperature for sineteringtherein using microwave.
 3. The manufacturing technique for powdermetallurgy in accordance with claim 1, wherein ceramicmicrowave-absorbent medium containing the microwave-absorbent body ispowder mainly made of carbon, carbide, nitride, nitanate, oxide, sulfideor a compound.
 4. The manufacturing technique for powder metallurgy inaccordance with claim 3, wherein the carbide is SiC, TiC or WC.
 5. Themanufacturing technique for powder metallurgy in accordance with claim3, wherein the nitride is TiN, AlN or Si₃N₄.
 6. The manufacturingtechnique for powder metallurgy in accordance with claim 3, wherein thetitanate is barium titanate, calcium titanate, strontium titanate orlead titanate.
 7. The manufacturing technique for powder metallurgy inaccordance with claim 3, wherein the oxide is NiO, CoO, CaMnO₃, LaMnO₃,SnO₂, TiO₂, MgWO₄, MgO, NiO, SrTiO₃ or SrZrO₃, ZrO₂ or CaO.
 8. Themanufacturing technique for powder metallurgy in accordance with claim3, wherein the oxide is added with compounds such as Li₂O, La₂O₃, CaO,SrO, TiO₂, Sb₂O₅, Ta₂O₅ or Cr₂O₃ or ZnO.
 9. The manufacturing techniquefor powder metallurgy in accordance with claim 3, wherein the sulfide isFeS or MnS.
 10. The manufacturing technique for powder metallurgy inaccordance with claim 3, wherein the compound is Fe₂O₃—MeO.
 11. Themanufacturing technique for powder metallurgy in accordance with claim3, wherein the compound is Fe₂O₃—MeO, and the Fe₂O₃ may be mixed withNiO, CoO, MoO, MgO, ZnO, CuO, Li₂O, CaO, FeO, B₂O, PbO, SrO, La₂O₃,Cr2O₃, SnO₂ or WO₃.
 12. The manufacturing technique for powdermetallurgy in accordance with claim 3, wherein the NiO, CoO, MoO, MgO,ZnO, CuO, Li₂O, CaO, FeO, B₂O, PbO, SrO, La₂O₃, Cr₂O₃, SnO₂ or WO₃ maybe used independently or mixed with others.
 13. The manufacturingtechnique for powder metallurgy in accordance with claim 3, whereinceramic microwave-absorbent medium containing the microwave-absorbentbody may be compounds with any compound ratios from carbon, carbide,nitride, titanate, oxide, sulfide or a compound.
 14. The manufacturingtechnique for powder metallurgy in accordance with claim 1, wherein thenon microwave-absorbent medium is a compound having any compound ratiofrom Al₂O₃, SiO₂ or ZrO.
 15. The manufacturing technique for powdermetallurgy in accordance with claim 1, wherein the macromolecules arebinders, fillings or lubricant containing any from acrylic, ethylcellulose, hydroxypropyl cellulose, polypropylene, polyacetal polymer,ethylene vinyl acetate, atactic polypropylene,styrene-butadienecoplymer, methylcellulose, polyethylene, oxidizedpolyethylene, cellulose acetate, nylon, polystyrenes, polybutylene,polysulfone, polyethylene, paraffin, wax, mineral oil, vegetable oil,fatty acid, fatty alcohols, fatty ester hydrocarbon wax, epoxy,polyphenylene, phenol, stearic acid, ester wax, oleic acid, diethylphthalate, and formaldehyde.